1. Field of the Invention
The present invention generally relates to a charge pump circuit, and more particularly to a half-ratio charge pump circuit that generates an output voltage at approximately half the input voltage.
2. Description of Related Art
A charge pump circuit is one of power converters that convert a source of direct current (DC) from one voltage level to another voltage level. The charge pump circuit commonly uses capacitors as energy storage elements to generate either a higher or lower voltage power. The charge pump circuit may commonly be adopted at I/O level, for example, of a source driver for driving a liquid crystal display (LCD).
Multiple capacitors, typically known as flying capacitors, are required in the charge pump circuit for generating positive and negative output voltages, respectively. It is known that the capacitor with significant capacitance will occupy a substantial circuit area, which is unfavorable for an integrated circuit design.
High-voltage devices such as high-voltage transistors are also required in the charge pump circuit for obtaining a voltage level comparable with the I/O level, for example, of the source driver. In addition to their stringent design requirements, the high-voltage devices take up more layout area than low-voltage devices.
Low-dropout (LDO) regulator or circuit is commonly used to construct a power converter to generate an output voltage at half the input voltage adaptable to the source driver. One disadvantage of the LDO circuit, however, is its low power efficiency.
For the foregoing reasons, a need has arisen to propose a novel charge pump circuit for generating specific output voltages with simpler circuit architecture and less layout area.